Control grille assembly for colorkinescopes, etc.



y 1,1952 H. B. LAW 2, 02,145

CONTROL GRILLE ASSEMBLY FOR COLOR-KINESCOPES, ETC

Filed Aug. 25 1950 27* CUP/=55 ATTORNEY Patented July 1, 1952 CONTROL GRILLE ASSEMBLY FOR COLOR- KINESCOPES, ETC.

Harold B. Law, Princeton, N. J assignor .to Radio Corporation of America, a corporation of Delaware Appiication August 25, 1950, Serial No. 181,342

This invention relates to improvements in colorkinescopes and other types of electron-beam tubes wherein it is necessary or desirable to prevent the beam from departing even slightly from its normal or intended path-oi-scan.

Among the-factors tending to deflect an electron beam from its intended path-of-scan in a cathode-ray tube are (a) insufficient linearity in the deflection circuits (b) stray magnetic fields (c) misalignment of the electrodes and the deflection coils or yoke and (d) fluctuations in the electrical supply lines for the tube. The degree and duration of departure which can be tolerated depends to some extent upon the use to which the tube is put. Thus if the beam of a conventional oscilloscope departs a fraction of an inch from its intended path the inaccuracies may go unobserved. On the other hand, a similar deviation in the path of scan in color-kinescopes or other beam tubes of the type wherein the screen is divided into elemental or subelemental areas will ordinarily result in color dilution or other false reading.

This problem has long been recognized and numerous ingenious electrode arrangements and control circuits have been devised to solve it. Thus, Zworykin in U. S. Patent 2,415,059 teaches the use of control signals generated ina number oi photocells to achieve beam-to-line registry in a color kinescope. Each photocell in the Zworykin system is sensitive to one of the colors emitted by the phosphor lines; and the control signals are employed to accelerate or decelerate the deflection of the beam in accordance with its departure from the color being scanned. They thus serve to retain the instantaneous line deflection path of the scanning beam on that line. Donald S. Bond in copending U. S. application Serial Number 146,282, dated February 25, 1950, adopts a difierent approach. He provides a signal generating area along a marginal edge of an electron sensitive target. If the electron beam should be out of register as it starts to scan a given line, seeondary-emissive signal areas above and below the correct starting point initiate a signal of proper direction and proportion to provide adequate voltage on a Vernier deflecting means to bring the electron beam into registry as it scans the line.

Zworykins photo-electric beam control system, described above, has the advantage of maintaining its control throughout the scanning interval, but the amplitude of its control signals depends upon the intensity of the light which'the 8 Claims. (Cl. 31392) photocells pick up from the screen. As a consequence, only weak control signals are available when a dark area is being televised. Bond's system does not depend upon light intensity, but control is applied only at the instant when the electron beam starts each scanning line. It is not a continuous process.

Accordingly, the principal object of the present invention is to obviate the foregoing and other less apparent objections to present day electron-beam tubes of the scanning variety.

Another and related object is to provide a targetassembly for a cathode ray tube which will keep the scanning beam in register with the line being scanned, throughout the scanning interval.

A further object is to provide a control structure or assembly which can be utilized to correct both horizontal and vertical distortion of a scanning raster.

Stated generally, the invention consists of interposing a bi-part control grille of special construction between the electron source and the line screen. This grille provides corrective signals which are utilized to bring the scanning electron beam back into register if it strays from its proper scanning line.

The invention is described in greater detail in connection with the accompanying drawing,

wherein:

Fig. 1 shows a cathode ray tube containing a target assembly constructed in accordance with the principle of the invention and including an appropriate circuit means for applying the correcting signals to the deflecting plates within the tube.

Fig. 2 is a view of the grille and screen assembly as viewed from its target side.

The drawing shows the invention as applied to a color kinescope of the line screen variety. The tube shown is of conventional shape and dimensions, and comprises an evacuated envelope I having a main chamber 3 in the form of a frustrum which contains the electron-sensitive screen 5 and bi-part control grille l-9 assembly of the invention. The neck portion ll of the tube contains a pair of horizontally disposed defleeting plates l3-I5 and an electron-gun consisting of an indirectly heated cathode ii, a grid 19 and an anode 2|.

The screen comprises. a transparent or translucent foundation plate 5 which contains a multiplicity of phosphor lines 1", b and g of elemental width dimensions on its rear or "target surface.

These lines are arranged in groups of (say three) and extend horizontally across the plate, 1. e.v

may be unbroken from thebeginning to end, or

they may be made up of a multiplicity of phosphor dots.

The control grille 1-9 comprises a first set of wires 1 extending parallel to each other and at an angle of approximately 45 with respect to the phosphor lines 1-, b, g on the foundation plate 5. A second set of wires 9, electrically independent of the first set, extends at an angle of approximately 45 with respect to the phosphor lines in the appropriate direction (i. e. at the approximately 90 with respect to the wires of the first set). Thus the wires 1 of the first set may be said to have a positive slope with respect to the phosphor lines r, b and g and the wires 9 of the second set a negative slope with reference to said phosphor lines.

This grille structure may be placed in contact with the electron-sensitive surface of the screen 5 and follow its contour, or it may be spaced from it, as shown. The number of wires in each set corresponds substantially to the number of parallel electron-sensitive lines on the screen '5.

These sets of wires, as shown more clearly in lfig. 2, have the points at which the wires of the set '9 cross the wires of the set I in register with the phosphor lines 1, b and g of the screen 5. Consequently, if the scanning electron beam passes over successive junctions of the two sets along a given axis of intersection, it will be in constant register with the phosphor line corresponding to that axis. 1

If the beam should wander in the upward direction off an axis of intersection of the wires I and 9 the second set of wires '9 (i. e. the ones with the negative slope) will receive the impact of the beam 23 before the first or positive set of wires i. Should the beam wander in the downward direction off an axis of intersection of the wires l and 9 the first set of wires (i. e. the ones with the positive slope) will receive the impact ahead of the second set 9. The signals thus generated in the individual sets of wires 1 and 9 are used (in the manner described below) to return the beam, in the proper direction, to its normal path.

The present invention is not concerned with the particular form of circuit which may be employed for converting the signals picked-up by the grille 'I9 into Vernier deflecting forces for correcting the path of the beam 23. However, one circuit, suitable for the purpose, is shown by way of example. The circuit here shown comprises a separate amplifier 25, 25 and clipper 2'1, 27' for each of the two setsoflwires 1 and 9 of which the grilleis comprised.

If the scanning beam is out of register with the axis of intersection of the Wires] and 9 and consequently strikes the wires of one. set before the wires of the other, a signal-is fed through the appropriate amplifier and clipper to the control grid of one of the tubes 29, 29'. This causes that tube to conduct and drain the charge from a condenser 3I which is common to the cathode circuits of both tubes. When a signal arrives at the other tube the charge on the condenser (H is not available for it to draw upon. As a result unequal voltages are applied to the deflection plates I3 and I 5, and the beam is subjected to a Vernier correcting force of a sign and intensity calculated to restore it to its normal path.

The output of the tubes 29, 29 could be applied to the main deflecting coil 33 on the neck of the tube instead of to the'deflecting plates I3 and I 5. However applying the Vernier correcting voltages to the deflecting plates avoids the lag incident to the inductive inertia of the coil 33.

The horizontal phosphor-dine screen shown in the drawing may be used in either a frame or line sequential television system. The Vernier vertical deflection system above described ensures color purity. It will be apparent that to adapt the screen to the dot or element sequential system each phosphor'line must be broken up into a succession of difierently colored (e. g. red, blue and green) dots. The bi-part grille structure of the present invention may be used in conjunction with a correcting circuit similar to the one shown in Beers U. S. Patent No. 2,385,563 to prevent horizontal distortion of the scanning raster when the dot-sequential system is employed. In such a circuit the velocity with which the scanning beam crosses the signal wires is converted into a frequency which is compared with a standard reference frequency.

Any difference in the two frequencies is converted into a control potential which is used to restore the scanning velocity to its normal value. If desired, two correcting circuits may be employed, one utilizing the herein described timedifferences in the grille signals to correct for vertical non-linearity and the other pulse-frequency differences to correct for horizontal distortion.

In conclusion, attention is called to the fact that since the correcting signals from the bipart grille of the invention are in no way dependent upon the color of the phosphor lines on the screen, the invention is applicable to cathoderay tubes containing various other types of linescreens.

What is claimed is:

1. A target-assembly for a cathode-ray tube comprising a foundation member, electron-sensitive materials disposed in parallel lines upon a surface of said foundation member, a first set of parallel wires mounted adjacent to said surface and extending there across at an angle of substantially with respect to said lines of electron-sensitive materials, and a second set of parallel Wires disposed in front of said first set and extending thereacross at an angle of substantially with respect to said first mentioned wires. 7

2. The invention as set forth in claim 1 and wherein the number of wires in each of said first and second sets corresponds substantially to the number of parallel lines of electron-sensitive materials on said foundation surface.

3. The invention as set forth in claim 1 and wherein the axes of intersection of the wires of said first and second sets lie in register with said lines of electron-sensitive materials.

4. A target assembly for a color-kinescope, said assembly comprising; a foundation member containing amultiplicity of parallel phosphorlines on a surface thereof, said lines being constituted of difierent phosphor materials each capable of emitting light of a particular color when struck by electrons, adjacent ones of said parallel phosphor lines having different coloremissive characteristics, and a bi-part grille comprising two electrically independent sets of parallel wires disposed diagonally with respect to said phosphor lines and at an angle of substantially 90 with respect to each other, the number of wires in each of said sets corresponding substantially to the total number of phosphor lines of a given one of said color characteristics.

5. The invention as set forth in claim 4 and wherein the axes of intersection of said first and second sets each lie in register with the phosphor lines of said given one of said colors.

6. In a cathode-ray tube, the combination with a target of the line-screen variety of a control grille assembly comprising two electrically independent sets of parallel wires disposed diagonally with respect to the lines on said screen and at an angle of substantially 90 with respect to each other.

7. A cathode ray tube comprising an evacuated envelope containing an electron-beam source, a foundation member, electron-sensitive materials disposed in the form of parallel lines upon a surface of said foundation member in the path of the beam from said source, a bi-part control grille assembly disposed between said source and said foundation surface, said control grille assembly comprising two sets of parallel wires disposed diagonally with respect to said electron-sensitive lines and at an angle of substantially 90 with respect to each other in the path of said beam, and a pair of deflecting plates disposed on opposite sides of the path of said beam between said beam source and said control grille assembly for applying to said beam Vernier deflecting forces derived from the impact of said beam upon the wires of which said control grille assembly is comprised.

8. The invention as set forth in claim '7 wherein the electron-sensitive lines extend across said foundation surface in a horizontal direction and said deflecting plates are disposed in parallel relation with respect to said horizontally disposed lines.

HAROLD B. LAW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,814,805 Hitchcock July 14, 1931 2,343,825 Wilson Mar. 7, 1944 2,446,249 Schroeder Aug. 3, 1948 2,446,440 Swedlund Aug. 3, 1948 2,461,515 Bronwell Feb. 15, 1949 2,490,812 Huffman Dec. 13, 1949 2,498,705 Parker Feb. 28, 1950 2,518,200 Sziklai et al. Aug. 8, 1950 2,543,477 Sziklai et a1 Feb. 27, 1951 

